Actuator systems employing energy recovery techniques

ABSTRACT

A system for accelerating and decelerating a movable element of an actuator includes an inductive energy storage means, a circuit for producing a predetermined current condition in the inductor which holds the element in a balanced position and stores energy in the storage means, and switch means for discharging the storage means through the actuator to accelerate the element. The back E.M.F. developed by the motion of the element produces a current which opposes the accelerating current and thus applies to the energy store kinetic energy developed by the movement of the element.

ilmteul tates Patent 1 1 1111 3,729,663

Stevenson et al. 1451 Apr. 24, 1973 ACTUATOR SYSTEMS EMPLOYING 3,560,821 2/1971 Beling ..318/138 ENE G RECOVERY TECHNIQUES 3,465,233 9/1969 Johnson eta1.. ..321/45 R 3,474,322 10/1969 King ..321/45 R Inventors: Timothy J Stevenson, Wmdsor; 3,449,654 6/1969 Sheldrake et a1. ..321/5 13 Gordon George Scarrott, Welwyn 3,560,818 2/1971 Amato ....321/45 ER Garden City, both of England 3,530,347 9/1970 Newell ..318/138 [73] Assignee: international Computers Limited, Primary Examiner D R Duggan London England Att0rneyFrederick E. Hane et al.

[22] Filed: Aug. 2, 1971 [21] Appl.No.: 168,102

[57] ABSTRACT A system for accelerating and decelerating a movable element of an actuator includes an inductive energy [30] Foreign Application Priority Data storage means, a circuit for producing a predetermined current condition in the inductor which holds the element in a balanced position and stores energy in the storage means, and switch means for discharging the storage means through the actuator to ac- Sept. 4, 1970 Great Britain ..42,368/74 [52] US. Cl. .1 ....318/135, 318/687, 321/45 lift. (Il. celerate the element. The back developed [58] Field of Search ..321/5 B, 45 R, 45 ER; the motion of the element produces a Current which 310/1244; 318/687, 135, 8307/7183, opposes the accelerating current and thus applies to 72 the energy store kinetic energy developed by the movement of the element. [56] References Cited 5 Claims, 1 Drawing Figure UNITED STATES PATENTS 3,406,328 lO/l968 Studtmann ..318/138 X POW ER 12/ SOURCE 25 ACTUATOR CONTROL CARQKHT POWER SOURCE ,/-Z3

Patented April 24, 1973 .CDUMZU JOMFFZOU MHZ/0n,

-INVENTORS Gong? lens: GQRIGTT ATTORNEYS ACTUATOR SYSTEMS EMPLOYING ENERGY RECOVERY TECHNIQUES BACKGROUND OF INVENTION head from one track on the disc to another. One limitation on the speed at which data on a disc may be accessed therefore, is the time necessary to position the recording head. Also, the speed at which the recording head may be moved is limited since the power for driving the recording head and associated carriage mechanism must be provided economically. Since, in practice, the power necessary to effect motion of the head and carriage, or to operate an actuator, rises rapidly with the inverse cube of the time in which the motion is to take place, it becomes important to provide the power as economically as possible.

It has previously been known to provide the necessary kinetic energy to operate an actuator by drawing electric power by way of control circuits from a power supply. As the actuator is decelerated, the kinetic energy of the actuator is dissipated in, .for example, transistors and resistors, of the control circuitry between the power source and the actuator. It is also known, for example, in circuits for energizing a winding of a magnetic recording head, to provide an inductor with a predetermined current normally flowing therethrough. This inductor may be termed an assisting inductor because when it is necessary to. energize a head winding, this current is rapidly switched to the head winding and thereby assists in causing the current in the head winding to reach its maximum value. While an assisting inductor acts to apply a step function voltage to the recording head and thus reduce the time necessary for the current in the head winding to reach its maximum value, the circuit elements must absorb this current upon dissipation of the recording field. Consequently, the electrical power necessary to energize the head winding is not being economically employed as a result of being dissipated in the circuit elements.

SUMMARY OF THE INVENTION According to the present invention there is provided a system for controlling movement of the movable element of an actuator including an inductive energy storage means, circuit means for producing a predetermined current condition in the storage means to establish a store of energy therein, means for discharging the energy storage means through the actuator to cause the actuator element to accelerate in a desired direction; and means for feeding to the storage means current arising from movement of the element in opposition to current accelerating the element thereby to apply kinetic energy developed by movement of the element to the energy storage means.

BRIEF DESCRIPTION OF THE DRAWING For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawing, in which the sole FIGURE shows in schematic form a system for accelerating and decelerating a movable element of an actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing, a control circuit 12 has a first output connected to the base of a transistor 10 by means of a line 22, and a second output connected to the base ofa transistor 11 by a line 23. An inductor 25 has a core element 20 and associated windings 16 and 17 so that the coils are coupled in a uniform polarized manner. To keep leakage inductance between the windings 16 and 17 to a minimum they may be wound in bifilar arrangement. The positive terminal ofa power source 18 is connected to the negative terminal of a power source 19. Both of these terminals are connected to the same input of an actuator 21. The negative terminal of the source 18 is connected to the upper end of the winding 17 while the positive terminal of the source 19 is connected to the lower end of the winding 16. The lower end of winding 17 is connected through a diode 14 to the collector of the transistor 11 while the upper end of the winding 16 is connected through a diode 15 to the collector of the transistor 10.

The other input of the actuator 21 is connected to the emitter electrodes of the transistors 10 and 11. The actuator 21 may, for example, be a linear motor employed in a magnetic disc head positioning system. This motor may be of the moving coil type as described in co-pending U.S. Pat. application Ser. No. 102772, filed Dec. 30, 1970, which application is assigned to the assignees of the present invention.

The operation of the system will now be described.

The actuator 21 includes a movable mass which is acted upon by a DC. motor producing a force proportional to the current in the motor. The mass-motor combination has an equivalent circuit whose dominant impedance component is capacitive. Consequently, the equivalent capacitance of the actuator can be regarded as forming part of a tuned circuit with the inductive impedance of the inductor 25 so that the actuator and the inductor can inter-exchange energy. One form of linear motor or actuator is illustrated in U.S. Pat. No. 3,260,870.

To maintain the actuator 21 in a stationary condition the control circuit 12 is arranged to produce output signals over the lines 22 and 23 to hold both of the transistors 10 and 11 in a conductive condition. The

power source 19 can then cause a current i, to flow through the winding 16, the transistor 10 and the actuator 21. At the same time the source 18 causes a current i which is arranged to be substantially equal to current I], to flow through the winding 17, the transistor 11 and the actuator. The currents i, and i flow in opposite directions in the actuator and since currents i and i: are substantially equal they effectively cancel one another in the actuator, so that the nett current flow through the actuator 21 is insufficient to energize the actuator to cause operation thereof. Even though the nett current flow through the actuator 21 is zero, the currents i and i will produce a standing current condition in the inductor so that a state of energy corresponding to the sum of i and i is established in the inductor.

The control unit 12 may be controlled by a servo system, which forms no part of the present invention, to control the currents i, and i by equal and opposite amounts whilst maintaining the required nett current condition through the actuator 21. Consequently the circuit 12 is able carefully to hold the actuator 21 stationary in the required position by making the appropriate changes in i, and i This mode of operation will, for example, allow a recording head (not shown) to be positioned adjacent to a single track on a mag netic disc (not shown).

When it is required to change, for example, the position of a recording head, the balanced current condition in the actuator has to be removed so that the actuator is to be energized. This may be effected by causing the control circuit 12 to pass an output over the line 23 which renders the transistor 11 non-conductive and the output over the line 22 holds the transistor conductive. The current flow i through the series circuit including the coil 17, the diode 14, the power source 18, the actuator 21, and the transistor 11 is interrupted, whilst the current continues to flow through the series circuit including the coil 16, the diode 15, the transistor 10, the actuator 21 and the power source 19; The inductor tries to maintain a total current flow of i plus i through the windings 16, 17 but with the circuit of winding 17 interrupted the current i cannot flow in winding 17 with the result that the inductor causes a current initially equal to current i to be added to the standing current i in winding 16 and therefore a nett current equal to 1', plus i flows through the actuator 21.

On receipt of this combined current i and i the actuator is accelerated in a first direction. During this acceleration energy is withdrawn from the inductor, so that the current component i falls.

The movement of the actuator generates a back E.M.F. which produces a current i acting in opposition to the driving current i and i so that at any instant the movement of the actuator is the resultant of the falling magnitude current i;, the current i from the source 19 and the opposing current i arising from the back E.M.F.

The algebraic sum of the currents i and i and i is progressively reducing until the current falls substantially to zero, as a consequence of the discharging of the inductor and the increase of the back E.M.F. arising from the acceleration.

When the inductor has travelled approximately half ofthe required distance through which it is to move the control circuit 12 is operated to reverse the conductive states of the transistors 10 and 11 so that the winding 16 is effectively switched out of circuit and the winding 17 is switched back into circuit. The current arising from the back E.M.F. generated by movement of the actuator 21 will now flow in the winding 17 in the same direction as the initial standing current i and result in building be able to build up the standing current condition in the inductor and the actuator will come to rest with the standing current in the inductor 25 restored to the initial value. That is to say the kinetic energy of the actuator has been applied to the inductor 25 rather than being dissipated in circuit elements such as the transistors 10 and 11.

Since the inductor 25 and the actuator 21 form part of a tuned circuit a clamped resonance condition is produced between the inductor and the actuator which latter acts as a capacitance with respect to the back E.M.F. thereby aiding the required energy transfer. As the back E.M.F. causes the current to be built up in the inductor 25, the actuator 21 is decelerated and comes to rest after moving a certain distance X. The distance X of motion of the actuator 21 is dependent upon the parameters ofthe actuator (or linear motor) and inductor 25. The actuator may be moved a shorter distance by causing the control circuit 12 to reverse the connections from the actuator 21 to the inductor 25 before the back E.M.F. causes the current to reach zero. The actuator may be moved a greater distance than distance X by disconnecting the actuator 21 from the inductor 25 for a period after the current has reached zero following acceleration of the actuator from its rest position. In this latter case, the control circuit 12 renders both the transistors 10 and 11 non-conductive. It will be appreciated however that both transistors may be rendered non-conductive simultaneously only when the current is zero, since a large voltage spike, which would damage the transistors 10 and 11, would be produced if the transistors 10 and 11 were open-circuited with a current flowing therethrough.

The requirements imposed on the power sources 18 and 19 are lower than if the kinetic energy of actuator 21 were simply dissipated in the circuit components. In the present system, the power sources 18 and 19 which are of nominally equal voltages, need only be able to produce a current and voltage sufficient to magnetize the inductor 25 and to make up for the resistive losses in the inductor 25 and in the transistors 10 and 11 and actuator 21. Such losses, however, are small in com parison to the total energy returned to the inductor 25 so that the total dissipation of power is kept to an economically low level.

After the actuator 21 has moved by the required distance, or the movable coil of a linear motor has moved by the required distance, the system can be returned to a stationary mode by continue to apply an output signal over the line 23 to hold the transistor 11 conductive and rendering the transistor 10 conductive by operating the control circuit 12 to apply an appropriate output signal over line 22. In this manner, the currents i and i are re-established.

It will be appreciated that the actuator 21 is energized to move in one direction by rendering the transistor 10 fully conductive and the transistor 11 nonconductive. Similarly, the control circuit 12 may apply output signals to render the transistor 10 non-conductive and transistor 11 conductive to energize the actuator 21 to cause motion in a reverse direction.

While the actuator 21 has been described as a moving coil linear motor, it will be appreciated that other forms of electrical motors may be employed. Thus, rather than moving a coil by a distance X, an armature may be moved by an angle if, for example, a suitable D.C. electric motor is used.

The diodes 14 and 15 are provided for the purpose of protecting the transistor 11 and 10 respectively, from back voltages developed by the transformer action between the windings l6 and 17 of the inductor 25.

While the transistor 10 and 11 are employed as switching devices, it will be realized that other semiconductor switching elements or thermionic valves may be employed as well.

We claim:

1. An actuator driving system including an actuator having an element movable in response to the application of an electric current to the actuator; an inductive energy storage device; first and second electrical power sources connected to the actuator to supply currents subtractively thereto and to the energy storage device to supply currents additively thereto; and control means effective in a first condition to cause the power sources to supply substantially equal currents and in a second condition to supply unequal currents, switching of the control means from the first to the second condition causing energy stored in the energy storage device to be delivered to the actuator.

2. A system as claimed in claim 1, including first and second current paths for respectively feeding first and second currents in opposite senses to the actuator to maintain the movable element in the quiescent condition and in the same sense to the inductive energy storage device to establish a predetermined energy level in the energy storage device, and in which the control means includes switch means for interrupting current flow through a selected one of said first and second paths so that current is fed to the actuator only through the other of the first and second paths and the energy storage device discharges through said other path to augment the current in said other path.

3. A system as claimed in claim 2, in which the switch means is operative to enable current flow through said selected path and to interrupt current flow in said other path so as to decelerate the element and transfer kinetic energy of the element to the storage device.

4. A system as claimed in claim 2, in which said inductive energy storage device includes a first winding connected in said first path and a second winding connected in said second path and a magnetic core effective to couple electromagnetically the first and second windings.

5. A system as claimed in claim 2 in which the switch means includes a transistor in each current path, and in which the control means is operable to adjust the conductive states of the transistors to change the conduction condition of the first and second paths. 

1. An actuator driving system including an actuator having an element movable in response to the application of an electric current to the actuator; an inductive energy storage device; first and second electrical power sources connected to the actuator to supply currents subtractively thereto and to the energy storage device to supply currents additively thereto; and control means effective in a first condition to cause the power sources to supply substantially equal currents and in a second condition to supply unequal currents, switching of the control means from the first to the second condition causing energy stored in the energy storage device to be delivered to the actuator.
 2. A system as claimed in claim 1, including first and second current paths for respectively feeding first and second currents in opposite senses to the actuator to maintain the movable element in the quiescent condition and in the same sense to the inductive energy storage device to establish a predetermined energy level in the energy storage device, and in which the control means includes switCh means for interrupting current flow through a selected one of said first and second paths so that current is fed to the actuator only through the other of the first and second paths and the energy storage device discharges through said other path to augment the current in said other path.
 3. A system as claimed in claim 2, in which the switch means is operative to enable current flow through said selected path and to interrupt current flow in said other path so as to decelerate the element and transfer kinetic energy of the element to the storage device.
 4. A system as claimed in claim 2, in which said inductive energy storage device includes a first winding connected in said first path and a second winding connected in said second path and a magnetic core effective to couple electromagnetically the first and second windings.
 5. A system as claimed in claim 2 in which the switch means includes a transistor in each current path, and in which the control means is operable to adjust the conductive states of the transistors to change the conduction condition of the first and second paths. 